The present invention relates to a coating method for use in a process for producing high-temperature superconductive strip conductors, which are required for high-temperature superconductor cables.
From the prior art,
1) IEEE Trans. Appl. Supercond. Vol. 5, No. 2 (1995), pp. 953-955,
2) Funjikamik et al. xe2x80x9c5m/2 KA High-TC-Cable Conductor,xe2x80x9d Adv. in Superconductivity V, pp. 1251-1254, Springer-Verlag 1993 (Transactions of the 5th International Symposium on Superconductivity, 1992),
3) Sato et al. xe2x80x9cElectromagnetic Properties and Structures of BiPbSrCaCuO Superconducting Wires,xe2x80x9d Advances in Superconductivity II, pp. 335-340, Springer-Verlag, 1990 (Transactions 2nd Int. Symp. on Superconductivity, 1989),
high-temperature superconductor cables that are composed of a plurality of strip conductors are known. These strip conductors, in turn, are made of a known high-temperature superconducting ceramic material, e.g., (Bi,Pb)2Sr2Ca2CU3OX, which is preferably contained in a silver matrix. In the finished cable, these silver matrix strip conductors are applied, e.g., stranded, to a carrier, e.g., a corrugated tube, and are soldered at their ends for contact.
From EPO 044 144 B1 it is known to provide conductors with an insulating ceramic outside layer to insulate the filamentary superconductor wires made of an intermetallic compound electrically with respect to one another, so that they can be wound into a magnet coil. This outer layer on the wires is produced in situ by applying an aqueous suspension of sodium silicate, kaolin and calcium carbonate, drying it and heat-treating it at a temperature in excess of 500xc2x0 C.
EP 0 322 619 A1 describes the application of a film between a carrier made, e.g., of strontium titanate, or also a metal, and its coating made of an oxide ceramic high-temperature superconducting material to ensure good adhesion between carrier and coating and prevent chemical reactions and interactions between carrier material and oxide ceramic material. For this interlayer, this document specifies aluminum oxide, among others, which is deposited on the carrier surface in the form of an alcoholic suspension and is sintered at 950xc2x0 C. to obtain a permanent connection with the carrier material.
In the production process, these strip conductors are sintered in known manner at correspondingly high temperatures. The strip conductors, or parts of these long strip conductors (several 100 m long) are helically wound onto an annealing base and are annealed lying next to one another. To prevent the strip conductors from sticking together or adhering during the required annealing processes, a coating of preferably aluminum oxide is provided on each individual strip conductor. This measure prevents the individual layers/windings of this strip conductor from sticking together/adhering at high temperatures in excess of 800xc2x0 C., at which the mechanical loadability of the silver is low.
To produce a superconductor cable, the finished strip conductors must be wound individually and bonded to corresponding terminals. For electrical bonding of each end of such a superconductor cable with terminals, the cable end and the terminal must be soldered together. For this purpose, it must be possible reliably to solder the individual strip conductors to the terminal. This is prevented, however, by the otherwise required aluminum oxide coating of the strip conductors. A solution must therefore be found to correct this incompatibility.